Tannase increases fruit set by interfering with self-incompatibility of Camellia oleifera

The fruit of Camellia oleifera has a wide range of industrial applications, but the self-incompatibility (SI) limits the fruit yield and restricts the development of C. oleifera industry. How to erase the SI of C. oleifera to increase fruit set is an urgent problem to be solved. In this study, tannase (TA), plant growth regulators, antioxidants, nitric oxide inhibitors, and epigenetic modification substances were used to treat self-pollinated C. oleifera, and the results showed that 5 g⋅L–1 TA could significantly improve the self-pollinated fruit setting rate by 16.06–22.33%. Fluorescence microscopy and paraffin section observation showed that TA treatment promoted the growth of self-pollen tube in C. oleifera, and significantly increased the ovule penetration (18.38%) and fertilization (16.18%). Pistil transcriptome analysis suggested that genes related to shikimic acid, gallic acid, phenylpropanoid, and flavonoid were significantly differentially expressed with the growth promotion of self-pollen tubes. TA treatment significantly increased flavonoids by 0.56 mg⋅g–1 and total polyphenols by 0.45 mg⋅g–1 in C. oleifera pistils compared to control, respectively, which was consistent with the trend of up-regulation of related gene expression. In addition, the results of the pollen in vitro germination test showed that high concentrations of shikimic acid, gallic acid, and epicatechin promoted the growth of pollen tubes within a certain concentration range. Cytoscape visualization suggested that MYBs, WRKYs, C2H2s, and other transcription factors interacted with the above key genes in response to TA treatment to regulate the accumulation of total polyphenols and flavonoids and the growth of self-pollen tubes, ultimately increasing fruit set. This study provides a new comprehensive understanding of exogenous TA on cell morphology, physiological changes, and gene expression regulation in C. oleifera, and provides useful references for the wide application of TA and the breaking of SI in other plants.